Adult neural stem/progenitor (NSP) cells can replace injured neurons, thereby suggesting that appropriately targeted manipulation of the NSP cells may contribute to effective therapies for trauma, stroke, neurodegenerative disease and aging. A prerequisite to any such therapies is a better understanding of the largely unknown mechanisms regulating adult NSP cells in vivo. Indirect data suggest, and we hypothesize, that endogenous ciliary neurotrophic factor (CNTF) receptor signaling inhibits the neuronal differentiation of NSP cells. Specific Aim 1: We have used a novel in vivo assay to identified functional CNTF receptors in subventricular zone (SVZ) NSP cells and anatomically characterize the responsive cells. The results indicate that SVZ type B stem cells are highly responsive. We will completely map the cellular distribution of the receptor and its ligands within the SVZ NSP cell niche with the functional assay and immunohistochemistry. Specific Aim 2: Our data indicate that disruption of in vivo CNTF receptor signaling in SVZ NSP cells, with a floxed CNTF receptor 1 (CNTFR1) mouse line and a gene construct driving Cre recombinase (Cre) expression in NSP cells, leads to increases in SVZ-associated neuroblasts and new olfactory bulb neurons, as well as a neuron subtype specific, adult-onset increase in total olfactory bulb neuron populations. Adult onset receptor disruption in SVZ NSP cells with a recombinant adeno-associated virus (AAV-Cre) also leads to increased neurogenesis. Together, the data indicate for the first time that endogenous CNTF receptor signaling regulates adult neurogenesis, and further suggest that the regulation occurs at the NSP cell stage in a neuron subtype specific manner. We will use the above tools and: 1) an inducible Cre gene construct, 2) a Moloney leukemia virus-based retrovirus that drives Cre expression (MLV-Cre) in a NSP cell type specific manner, and 3) multilabeling immunohistochemistry, to fully characterize how CNTF receptors regulate adult, endogenous neurogenesis, as well as NSP cell proliferation and maintenance. Specific Aim 3: We will similarly use the above techniques to pursue our pilot studies that suggest that endogenous CNTF receptor signaling regulates neurogenesis in the adult striatum following quinolinic acid (QA)-induced neurotoxic injury, possibly through insult-induced increases in CNTF and CNTF receptor dependent signaling in the SVZ. Specific Aim 4: Increases in SVZ NSP cells and striatal neurogenesis have been reported for the R6/2 genetic mouse model of Huntington's disease (HD) and for human HD itself, suggesting, along with our data, that disruption of CNTF receptor signaling in the NSP cells may significantly enhance this already elevated neurogenesis. We will directly text this possibility with R6/2 mice and the above techniques.